1. Field of the Invention
The present invention relates to earplugs serving as a hearing protection device or as a hearing aid. The earplug comprises a shell which is to be inserted at least in the outer part of the user's ear canal.
2. Description of Related Art
A large part of the population is exposed to hazardous noise from time to time. This can be at work, whilst traveling, during leisure activities or at home. The exposure can lead to permanent hearing loss, distract people's attention from other hazards or simply cause stress. In order to prevent both accidents and permanent hearing damage, hearing protection devices (HPDs) have been provided in many styles and over many years. It started with the earmuff which is still very relevant and addresses very noisy environments (e.g. airports, construction, shooting) or complex working/communication situations (e.g. fighter pilots). Over the years development of biocompatible soft materials has enabled soft earplugs in different styles and colors as well as recent development of “one fits many” standard semi-soft earplugs in silicon-rubber type materials. For severe situations even the combination of an earmuff and an “in-the-ear” HPD is required to achieve desired attenuation. The physical limitation of hearing protection based on ear worn devices is defined where bone-conduction (body acoustics) becomes dominant at around 40 dB attenuation.
A common disadvantage of the above mentioned HPD styles is wearing discomfort. In case of the earmuffs, they are large which creates difficulties in combination with other head worn gear and they “close off” the ear too much for most applications. The in-the-ear styles mentioned are devices made to fit “the average” ear in one way or the other. Either the fit is provided by softness of the material which leads to undefined device insertion and undefined attenuation, or the fit is provided by standard shaped structures intended to block off the ear canal. In both cases the flat distribution of the individual shape of the outer ear and the ear canal leads to bad fit, pressure points in the ear and undefined positioning of the device.
To address this wearing comfort issue, in-the-ear hearing aid technology has been applied making customized ear molds with passive acoustical filter. These are long lasting devices with good wearing comfort. However, this customization process is traditionally a very manual process creating varying results over time, low reproducibility and the quality is very operator skill dependent.
The fabrication of customized hard shells by use of a rapid prototyping technology, primarily for hearing aids is described, for example, in U.S. Pat. No. 6,533,062 B1 or U.S. 2003/0133583 A1.
The term “earplug” as used in the following should designate any object which comprises at least a portion which is to be worn at least in the outer portion of the user's ear canal in a manner that it is retained within the ear canal.
If an earplug is designed as an active hearing protection device or a hearing aid, it includes an electroacoustic output transducer (i.e. speaker or receiver) which converts audio signals into sound to be output at the inner (distal) end of the shell. The system further includes an electroacoustic input transducer (i.e. a microphone) which converts ambient sound into audio signals and an audio signal processing unit which may comprise, for example, an amplifier and electronic filters. In addition, the system comprises a power source (battery) which may be mounted at or within the shell. The microphone and the audio signal processing unit may be mounted at or within the shell or may be external to the earplug, with a wired or wireless connection to the output transducer being provided in the latter case.
If the earplug is designed as an active hearing protection device, the earplug provides for attenuation of ambient sound reaching the outer (proximal) end of the earplug, and the audio signal processing unit is designed such that the overall amplification is negative. In this case, the active components serve to temporarily or spectrally select the sound signals which should be perceived by the user, thereby by-passing the mechanical attenuation function.
If the earplug is designed as an in-the-ear hearing aid, the acoustical gain tends to be quite high, for example, up to 50 dB gain or 120 dB sound pressure level.
If the earplug is designed as a passive hearing protection device, it includes an acoustic filter element for attenuating sound received at the outer end of the earplug, but it does not include any active sound producing elements.
In general, an earplug may be made of a soft, resilient material in order to conform to the individual shape of the user's ear canal and outer ear.
In addition, it is known to measure or determine the inner shape of the user's ear canal and outer ear by producing an impression or by three-dimensional laser scanning and to produce an earplug with a shell having an outer surface which is individually shaped according to the user's ear canal and outer ear in order to improve wearing comfort and the retaining forces. Such individually shaped earplugs are commonly referred to as customized earplugs. Due to the improved fitting, the material of the shell of customized earplugs may be significantly harder than the material of standardized soft earplugs. One known method for producing the individually shaped shell is layer-by-layer laser sintering (selective laser sintering (SLS)) of an appropriate powder material such as polyamide, see for example U.S. Pat. No. 6,533,062 B1 or U.S. 2003/0133583 A1.
DE 196 34 984 A1 relates to a hearing aid having a multi-way output transducer which is located in a sound outlet passage of an earplug having an individual outer shape. The multi-way output transducer may comprise several identical or different electroacoustic transducers which are realized as a multi-layer foil transducer on a spiral band.
U.S. Pat. No. 5,692,059 relates to an active hearing protection device which comprises a microphone, an electroacoustic output transducer and an accelerometer for sensing vibrations. The device comprises a Y-shaped output tube with one of the branches being connected to the microphone and the other branch being connected to the output transducer.
U.S. Pat. No. 6,533,062 B1 relates to a customized earplug having a shell formed by selective laser sintering, which may form a hearing aid or a hearing protection device. The shell includes integrated venting channels and specifically shaped sound input tubes to the microphone. For the case of a hearing aid function it is described that these input tubes may comprise acoustic adapters in the form of specifically shaped lines or tubes which serve for tuning the acoustic impedance of the input tube. It is also described that venting channels may serve as acoustic conductors for acoustic impedance tuning. A similar disclosure is found in U.S. Pat. No. 6,484,842 B1. Further, these documents disclose that the outer part of the shell may be made of a softer material than the inner part, with the outer part comprising a cavity for receiving an electronic module including the output transducer which is held there by elastic forces.
WO 02/01794 A1 relates to a customized earplug comprising a shell made by SLS, which may serve as a hearing aid or a hearing protection device, with venting tubes and a sound channel being integrated within the shell.
DE 100 41 733 A1 relates to a customized hearing protection device earplug which may include an active version. It is described in this document that mechanical frequency tuning may be achieved by filter selection, by selection of a venting tube with variable diameter and by providing the outer end of the shell as a resonance cavity.
DE 100 46 202 A1 relates to a customized earplug into which an output transducer is integrated by being directly fixed to the shell in a corresponding cavity. The microphone for providing an audio signal to the output transducer is remote from the earplug.
Due to the relatively high amplification in hearing aids the output transducer has to be mechanically decoupled from the microphone in order to avoid feedback problems due to vibrations transmitted from the output transducer to the microphone. Therefore it is common to provide for a soft mounting of the output transducer within the shell, for example by embedding the output transducer in an elastic material, see, for example, U.S. Pat. No. 4,969,534 or U.S. Pat. No. 4,729,451.
U.S. Pat. No. 6,585,075 B1 relates to a hearing aid in which the output transducer is hard mounted to the shell. In order to compensate for the vibration of the output transducer, the portion of the shell at which the output transducer is mounted is surrounded with an energy adsorbing soft material.
U.S. 2003/0112990 relates to a hearing protection or hearing aid earplug consisting of a core element surrounded by sleeve which is filled with a curable rubber-like material having a hardness value of less than shore A-30 for individually adapting the earplug to the shape of the user's ear canal and outer ear. The core element comprises a first sound bore which extends through the earplug and which may be detachably connected at its proximal end with a remote measurement apparatus and a second sound bore which is parallel to the first sound bore and which may be closed by an attenuation element or may serve as sound input by a hearing aid unit.
It is one object of the invention to provide for an active hearing protection earplug which provides for an optimized sound output.
It is a second object of the invention to provide for a method for manufacturing an earplug with an output transducer, which provides for an optimized sound output.
It is a third object of the invention to provide for a customized active hearing protection earplug which can be assembled in an easy manner and which allows for a defined positioning of the output transducer.
It is a fourth object of the invention to provide for a hearing protection earplug which allows for external control of the operation of the hearing protection earplug when worn by the user, in particular in order to control the sound attenuation function.
It is a fifth object of the invention to provide for a hearing protection earplug which ensures, other than by electronic peak clipping means, that the sound pressure level at a sound outlet opening at the inner end of the earplug does not exceed a predefined threshold value.